Zato

November 16, 2018

This post describes a couple of new techniques that
Zato
3.0 employs to make API servers start up faster.

When a Zato server starts, it carries out a series of steps, one of which is deployment of internal API services. There are 550+ of internal services, which means 550+ of individual features that can be made use of -
REST,
publish/subscribe,
SSO,
AMQP,
IBM MQ,
Cassandra,
caching,
SAPOdoo,
and hundreds more pieces are available.

Yet, what internal services have in common is that they change relatively infrequently. They do change from time to time but this does not happen very often. This realization led to the creation of a start-up cache of internal services.

Auto-caching on first deployment

Observe the output when a server is started right after installation, with all the internal services about to be deployed along with some of the user-defined ones.

In this particular case, the server needed around 8.5 second to deploy its internal services but while it was doing it, it also cached them all for later use.

Now, when the same server is stopped and started again, the output will be different. Nothing changed as far as user-defined services go but things changed with regards to the internal ones - not only did the server deploy the internal services but it also did it by re-using the cache created above and, consequently, 3 seconds were needed to deploy them.

Such a cache of internal services is created and maintained by Zato automatically, no user action is required.

Disabling internal services

Auto-caching is already a nice improvement but it is possible to go one better. By default, servers deploy all of the internal services that exist - this is because users may want to choose in their projects any and all of the features that the internal services represent.

However, in practice, most projects will use a select few technologies, e.g. REST and AMQP, or REST, IBM MQ, SAP and ElasticSearch, or any other combination, but not all of what is possible.

This explains the addition of a new feature which allows one to disable all the internal services that are known not to be needed in a particular project.

When you open a given server's server.conf file, you will find entries in the [deploy_internal] stanza whose subset is below. Note that if your Zato 3.0 version does not have it, you can copy the stanza over from a newly created server.

The list contains not internal services as such but Python modules to which the services belong, each module concerns a particular feature or technology, AMQP, JMS IBM MQ, WebSockets, Amazon S3 and anything else. Thus, if something is not needed, you can simply change True to False for each module that is not used.

But, you need to keep in mind that all the internal services were already cached before so, having changed True to False in as many places as needed, we also need a way to recreate the cache.

This is done by specifying the --sync-internal flag when servers are started; observe below what happens when some of the internal services were disabled and the flag was provided.

All the user-defined services deployed as previously but the cache for the internal ones was recreated and only some of them were deployed, only the ones that were needed in this particular project, which happens to primarily include
REST,
WebSockets,
Vault
and
publish/subscribe.

Note that even without the cache, the server needed only 4.1 second to deploy internal services which neatly dovetails with the fact that previously it needed 8.5 to deploy roughly twice as many of them.

This also means that with the cache already in place, the services will be deployed even much faster, which is indeed the case below. This time the server deployed the internal services needed in this project in 1.3 second, which is much faster than the original 8.5 second.

This process can be applied as many times as needed, each time you need new functionality disabled or enabled, you just edit server.conf, restart servers and that is it, the caches will be populated automatically.

With some of the services disabled, a caveat is that parts of
web-admin
will not be able to list or manage connections whose backend services were taken out but this is to be expected, e.g. if FTP connections were disabled in server.conf then it will not be possible to access them in web-admin.

One final note is that --sync-internal should really only be used when needed. The rationale behind the start-up cache is to make the process faster so this flag should not be used all the time, rather, there are two cases where it needs to be used:

When changing which internal services to deploy, as detailed in this post

When applying updates to your Zato installation - some of the updates may change, delete or add new internal services, which is why the caches need to be recreated in such cases